Hybrid vehicle and method of controlling hybrid vehicle

ABSTRACT

In a hybrid vehicle of the present invention, an engine EG is subjected to feedback control to attain a target revolving speed NE*. In the case of malfunction of an inverter P 1  for a generator GN, operation of the inverter P 1  is stopped. When the generator GN is driven to rotate at a predetermined rotational speed, a counter electromotive force arises in a multiphase phase coil of the generator GN. When a motor MG is connected to the generator GN as a loading, electric current runs via a protection diode of the inverter P 1  to implement power generation by the generator GN. The electric power generated by the generator GN is directly consumed by the motor MG. This arrangement enables the quantity of power generation to balance the quantity of consumption. Here the revolving speed of the engine EG is varied according to the loading applied to the vehicle. The arrangement of the present invention thus enables the amount of electric power generated by one of the generator GN and the motor MG to balance the amount of electric power consumed by the other of the generator GN and the motor MG, thus attaining a drive of the hybrid vehicle without using a secondary battery.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hybrid vehicle and a method ofcontrolling the hybrid vehicle. More specifically the invention pertainsto a hybrid vehicle with an engine that outputs power through combustionof a fuel, a generator that generates electric power with at least partof the power output from the engine, and a motor that outputs power to adrive shaft of the vehicle, as well as a method of controlling such ahybrid vehicle.

2. Description of the Related Art

A diversity of hybrid vehicles have been proposed. The hybrid vehiclehas a motor that outputs electric power as a driving force, in additionto an engine that outputs power through combustion of a fuel, such asgasoline. The hybrid vehicle uses the engine as the final energy sourceand thus requires only the supply of gasoline or another fuel. It isaccordingly not required to socially provide new facilities andequipment, for example, power stations for charging batteries.

The hybrid vehicles are mainly classified into series hybrid vehiclesand parallel hybrid vehicles. The series hybrid vehicle uses all thepower output from the engine to drive a generator, accumulates theelectric power generated by the generator in a battery, and obtains therequired driving force to be output to the drive shaft from a motor,which is driven with the electric power accumulated in the battery. Theparallel hybrid vehicle has a three shaft-type power distributingmechanism or a pair-rotor motor to distribute the power of the engine,for example, a gasoline engine, and causes the power output from theengine to supply part of the driving force to be output to the driveshaft. In the parallel hybrid vehicle, the residual power that is notoutput to the drive shaft is used for power generation by the generator.The generated electric power is generally accumulated in a battery or ahigh-capacity capacitor.

The electric power accumulated in the secondary battery or thehigh-capacity capacitor is used to drive the vehicle while the engine isat a stop. When the engine is driven but the driving force of the enginedoes not satisfy all the required torque, the motor utilizes theaccumulated electric power to supplement the insufficient torque.

In the hybrid vehicle of the above structure, in the case of malfunctionof the secondary battery or the high-capacity capacitor that accumulatesthe electric power therein or in the case of malfunction of a chargingcircuit for charging the secondary battery or the high-capacitycapacitor, operation of the generator is not allowed. This makes afurther drive of the vehicle difficult. According to the principles ofthe hybrid vehicle, the vehicle can be driven by directly connecting thegenerator with the motor and driving the motor with the generatedelectric power. The drive mode in this state is called the battery-lessdrive mode. In the case where the vehicle is actually driven in thedirect connection of the generator with the motor, however, expectedabrupt variations in loading on the motor during a drive cause adiversity of problems and troubles. There is a possibility that theloading or the required power of the drive shaft during a drive abruptlydecreases within a very short time, due to racing of wheels or anybraking operation. In such cases, the electric current to be flown intothe motor also abruptly decreases within a very short time. The abruptdecrease in required electric current causes a high impedance in thegenerator that is driven in stationary state by the engine. Thisabruptly raises the voltage between terminals of the generator andcauses an unexpectedly high voltage to be applied to the circuit andexceed the rated power of the circuit.

In the actual state, these problems make the battery-less drive modesubstantially unpractical. It is difficult to actualize the limp homecapability that enables the vehicle to be anyway driven to a gas stationwhile the battery or its charging circuit malfunctions. Especially inthe case of malfunction of a switching element included in an inverterthat is connected to the generator to form the charging circuit, evenwhen the engine, the generator, and the motor are all normally operable,the vehicle is driven only with the electric power accumulated in thebattery. This undesirably leads to a restricted driving distance or alimited vehicle speed.

The secondary battery used in the hybrid vehicle is a high voltagebattery. Positive and negative power lines respectively have contacts tocut off the connection of the power lines with the secondary battery inthe inactive state. These contacts are kept open when the vehicle is notused or when some abnormality is detected in the battery. The openposition of the contacts prevents the high voltage of the secondarybattery from being applied to the power lines when not required. Thesecontacts are used to allow and forbid a large flow of electric currentand are thereby often subject to troubles like welding. The prior artarrangement accordingly connects the power line with a standard contactin parallel via a resistor for restricting the electric current and anauxiliary contact. The procedure first closes the auxiliary contact toallow a restricted flow of electric current and then closes the standardcontact.

In this prior art arrangement, however, there is still a possibilitythat the contact welds. In response to detection of a weld of thecontact in either one of the positive and negative power lines, theprior art arrangement prohibits the use of the secondary battery. If thecontinuous use of the secondary battery is allowed in the welding stateof one contact, the connection of the secondary battery with the powerlines can not be cut off in case of a weld of the other contact.

SUMMARY OF THE INVENTION

The object of the present invention is thus to attain a drive of ahybrid vehicle with an engine, a generator, and a motor mounted thereonwithout using a secondary battery.

At least part of the above and the other related objects is actualizedby a first hybrid vehicle with an engine, a generator, and a motormounted thereon, wherein the engine outputs power through combustion ofa fuel, the generator provided with permanent magnets generates electricpower with at least part of the power output from the engine, and themotor outputs power to a drive shaft of the hybrid vehicle. The firsthybrid vehicle includes: an engine control unit that feedback controls aquantity of the fuel injected to the engine to attain a specified targetrevolving speed of the engine; a power generation control unit thatcauses the generator to carry out power generation utilizing a counterelectromotive force; a loading detection unit that specifies a loadingapplied to the hybrid vehicle; a generator rotational speed variationunit that varies a rotational speed of the generator, based on thespecified loading; and a motor driving unit that drives the motor withthe electric power generated by the generator at the varying rotationalspeed.

There is also a method of controlling the hybrid vehicle, whichcorresponds to the arrangement of the first hybrid vehicle. The presentinvention is accordingly directed to a first method of controlling ahybrid vehicle, wherein an engine outputs power through combustion of afuel, a generator provided with permanent magnets generate electricpower with at least part of the power output from the engine, and amotor is driven with at least part of the electric power generated bythe generator, so as to output power to a drive shaft of the vehicle.The first method includes the steps of: feedback controlling a quantityof the fuel injected to the engine to attain a specified targetrevolving speed of the engine; causing the generator to carry out powergeneration utilizing a counter electromotive force; specifying a loadingapplied to the hybrid vehicle; varying a rotational speed of thegenerator, based on the specified loading; and driving the motor withthe electric power generated by the generator at the varying rotationalspeed.

The first hybrid vehicle of the present invention or the correspondingfirst method of controlling the hybrid vehicle feedback controls thequantity of the fuel injected to the engine, in order to make the actualrevolving speed of the engine coincident with a specified targetrevolving speed. This arrangement effectively prevents the revolvingspeed of the engine from varying with a variation in loading of thegenerator, which generates electric power with at least part of thepower output from the engine. While the generator carries out powergeneration utilizing a counter electromotive force, the motor consumesthe electric power generated by the generator and carries out the poweroperation. The rotational speed of the generator is varied according tothe loading applied to the vehicle. This arrangement enables theadequate power corresponding to the loading of the vehicle to be outputto the drive shaft of the vehicle. The arrangement of varying therotational speed of the generator with a variation in loading applied tothe vehicle effectively prevents the rotational speed of the generatorfrom being unnecessarily heightened under the condition of low loading.

In accordance with one preferable application of the present invention,the hybrid vehicle further includes: an inverter that switches electriccurrent running through a multiphase coil of the generator; and asecondary battery that is charged with the direct current converted bythe switching operation of the inverter. The control procedure causesthe power generation control unit, the generator rotational speedvariation unit, and the motor driving unit to implement their functions,in response to detection of an abnormal state, which does not allow thesecondary battery to be charged via the inverter. The power generationutilizing the counter electromotive force has stricter restrictions, forexample, on the maximum power generation, compared with the powergeneration utilizing the inverter. The power generation utilizing thecounter electromotive force is accordingly carried out in the state thatdoes not allow the secondary battery to be charged via the inverter.

In the hybrid vehicle of the above application, when an observed voltagelevel of the secondary battery is higher than the counter electromotiveforce utilized for the power generation via the power generation controlunit, one preferable arrangement prohibits the power generationutilizing the counter electromotive force via the power generationcontrol unit but drives the motor with electric power accumulated in thesecondary battery. In the case where the secondary battery has asufficiently high voltage level as its state of charge, the motor may bedriven with the electric power taken out of the secondary battery.During a drive of the hybrid vehicle, the secondary battery may becharged with the regenerative electric power. In such cases, the hybridvehicle advantageously uses engine brake.

In the first hybrid vehicle of the present invention, the targetrevolving speed of the engine may be specified, based on behavior of anaccelerator pedal. The behavior of the accelerator pedal is highlycorrelated to the power requirement of the vehicle expected in the nearfuture. For example, depression of the accelerator pedal leads to anincrease in required power to be output to the drive shaft. Thearrangement of specifying the target revolving speed of the engine bytaking into account such correlation enables the upper limit of energyoutput from the engine to be adjusted at an earlier timing. Onepreferable procedure increases the rotational speed of the generatorwith an increase in amount of depression of the accelerator pedal. Thequick response to the increase in amount of depression of theaccelerator pedal significantly improves the drivability.

In accordance with another preferable application of the presentinvention, the target revolving speed of the engine is lowered or raisedin response to detection of an increasing tendency or a decreasingtendency of an actual revolving speed of the engine relative to thetarget revolving speed of the engine. The engine is under the feedbackcontrol to attain the target revolving speed. Controlling the drivingstate of the generator instantaneously increases or decreases the actualrevolving speed of the engine. The control procedure of this applicationlowers or increases the target revolving speed of the engine in responseto a variation in actual revolving speed of the engine. This anticipatesa variation in loading in the near future. Such control is especiallyeffective when separate control units are in charge of control of theengine and control of the generator and the motor and there is someinterference with transmission of the target revolving speed between theseparate control units, for example, via communication. The controlprocedure of this application may, however, be adopted in otherstructures that do not require transmission of the target revolvingspeed in such manner.

In the hybrid vehicle of the above application, one preferable controlprocedure urges the power generation utilizing the counter electromotiveforce, when an external force makes the drive shaft inversely rotatedand the motor fall into a state of power generation. When there is aninsufficiency of torque output from the vehicle, for example, running ona steep ascent, the vehicle may go back. In such cases, the drive shaftis inversely rotated and the motor falls into the state of powergeneration. The above control procedure desirably prevents over-voltagein such cases.

In the first hybrid vehicle of the present invention, one preferablecontrol procedure sets a maximum electric power generated by thegenerator with the power of the engine, specifies driving electric powerconsumed for driving the motor within the preset maximum electric power,based on the specified loading. The control procedure drives thegenerator to generate electric power that is equivalent to the drivingelectric power consumed by the motor, and regulates the electric currentrunning through a multiphase coil of the motor with the generatedelectric power. The control procedure of this application sets themaximum electric power generated by the generator and ensures thebalance of the generated electric power with the consumed electric powerwithin the preset maximum electric power.

The present invention is also directed to a second hybrid vehicle withan engine, a generator, and a motor mounted thereon, wherein the engineoutputs power through combustion of a fuel, the generator generateselectric power with at least part of the power output from the engine,and the motor outputs power to a drive shaft of the hybrid vehicle. Thesecond hybrid vehicle includes: an engine control unit that feedbackcontrols a quantity of the fuel injected to the engine to attain aspecified target revolving speed of the engine; a generative energycomputation unit that computes an instantaneous magnitude of generativeenergy to be generated by the generator by taking into account an energybalance in a system including the engine, the generator, and the motor;a voltage measurement unit that measures a generative voltage of thegenerator; a control variable computation unit that computes a feedbackcontrol variable corresponding to a difference between the observedgenerative voltage and a target generative voltage of the generator; agenerator control unit that feedback controls the generator with thecalculated instantaneous magnitude of generative energy and thecalculated feedback control variable; a requirement detection unit thatdetects a requirement on a drive of the vehicle; and a motor drivingunit that calculates an output torque of the motor based on a directtorque output from the generator, which is under control of thegenerator control unit, and a required torque related to the detectedrequirement on the drive of the vehicle, and drives the motor to attainthe calculated output torque.

There is also a method of controlling the hybrid vehicle, whichcorresponds to the arrangement of the second hybrid vehicle. The presentinvention is accordingly directed to a second method of controlling ahybrid vehicle, wherein an engine outputs power through combustion of afuel, a generator provided with permanent magnets generate electricpower with at least part of the power output from the engine, and amotor is driven with at least part of the electric power generated bythe generator, so as to output power to a drive shaft of the vehicle.The second method includes the steps of: feedback controlling a quantityof the fuel injected to the engine to attain a specified targetrevolving speed of the engine; computing an instantaneous magnitude ofgenerative energy to be generated by the generator by taking intoaccount an energy balance in a system including the engine, thegenerator, and the motor; measuring a generative voltage of thegenerator; computing a feedback control variable corresponding to adifference between the observed generative voltage and a targetgenerative voltage of the generator; feedback controlling the generatorwith the calculated instantaneous magnitude of generative energy and thecalculated feedback control variable; detecting a requirement on a driveof the vehicle; and calculating an output torque of the motor based on adirect torque output from the generator, which is under control of thegenerator control unit, and a required torque related to the detectedrequirement on the drive of the vehicle, and driving the motor to attainthe calculated output torque.

The second hybrid vehicle of the present invention or the correspondingsecond method of controlling the hybrid vehicle carries out the controlaccording to the calculated instantaneous magnitude of generative energyto be generated by the generator as well as according to the calculatedfeedback control variable. The instantaneous magnitude of generativeenergy is calculated by taking into account the energy balance in thesystem including the engine, the generator, and the motor. The feedbackcontrol variable is calculated corresponds to the difference between theobserved generative voltage of the generator and a target generativevoltage. Even when the generative voltage of the generator varies with avariation in loading, this arrangement ensures the quick response tosuch a variation and makes the quantity of energy generation balancewith the quantity of energy consumption. This enables the hybrid vehicleto be driven without charging or discharging the secondary battery.

In accordance with one preferable application of the present invention,the generator uses permanent magnets to form a magnetic field, and thehybrid vehicle further includes: an inverter that switches electriccurrent running through a multiphase coil of the generator; a secondarybattery that is charged with the direct current converted by theswitching operation of the inverter. The control procedure stops theswitching operation of the inverter and causes the generator to carryout power generation utilizing a counter electromotive force, inresponse to detection of a state of failure in feedback control of thegenerator using the feedback control variable. In the case where thefeedback control of the generator falls into the state of failure, thisarrangement quickly stops this feedback control and causes the generatorto carry out power generation utilizing the counter electromotive force.This arrangement effectively prevents the failure of the whole control.Although there is the upper limit, the power generation utilizing thecounter electromotive force enables the power generation according tothe quantity of power consumption and thereby makes the quantity ofenergy generation balance with the quantity of energy consumption. Inthe case where the feedback control of the generator through theswitching operation of the inverter falls into the state of failure dueto some disturbance, the temporary shift to the power generationutilizing the counter electromotive force effectively recovers the totalstate of control.

In the second hybrid vehicle of the present invention, in a specificdriving state where the motor generates electric power, for example, inthe course of braking, one preferable control procedure stops the fuelinjection to the engine and causes the generator to motor the engine andthereby consume the electric power generated by the motor. Thisarrangement enables the hybrid vehicle to use engine brake.

The present invention is also directed to a third hybrid vehicle with anengine, a generator, and a motor mounted thereon, wherein the engineoutputs power through combustion of a fuel, the generator generateselectric power with at least part of the power output from the engine,and the motor outputs power to a drive shaft of the hybrid vehicle. Thethird hybrid vehicle includes: an engine control unit that feedbackcontrols a quantity of the fuel injected to the engine to attain aspecified target revolving speed of the engine; a secondary battery thatis connectable with both positive and negative power lines of a directvoltage source, which link the generator with the motor; a first contactthat switches on and off connection of the secondary battery with one ofthe two power lines and links the secondary battery with the power linevia a restriction resistor, which restricts electric current flowing outof the secondary battery; a second contact that is connected to thefirst contact in parallel and directly links the secondary battery withthe power line; a third contact that switches on and off connection ofthe secondary battery with the other of the two power lines; a welddetection unit that detects a weld of the third contact; and awelding-state driving unit that opens both the first contact and thesecond contact after activation of the engine in response to detectionof the weld of the third contact, and drives the motor with the electricpower generated by the generator.

There is also a method of controlling the hybrid vehicle, whichcorresponds to the arrangement of the third hybrid vehicle. The presentinvention is accordingly directed to a third method of controlling ahybrid vehicle, wherein an engine outputs power through combustion of afuel, a generator provided with permanent magnets generate electricpower with at least part of the power output from the engine, and amotor is driven with at least part of the electric power generated bythe generator, so as to output power to a drive shaft of the vehicle.The third method includes the steps of: connecting a secondary batterywith both positive and negative power lines of a direct voltage source,which link the generator with the motor; interposing a first contactbetween the secondary battery and one of the two power lines via arestriction resistor, which restricts electric current flowing out ofthe secondary battery; connecting a second contact to the first contactin parallel, the second contact directly linking the secondary batterywith the power line: interposing a third contact between the secondarybattery and the other of the two power lines; feedback controlling aquantity of the fuel injected to the engine to attain a specified targetrevolving speed of the engine; detecting a weld of the third contact;and opening both the first contact and the second contact afteractivation of the engine in response to detection of the weld of thethird contact, and driving the motor with the electric power generatedby the generator.

In the third hybrid vehicle of the present invention or thecorresponding third method of controlling the hybrid vehicle, even whenthe third contact welds, once the engine is activated, the controlprocedure opens the first contact and the second contact and drives themotor with the electric power generated by the generator. Thisarrangement cuts off the connection of the power line with the secondarybattery and thus protects the first contact and the second contact fromwelding during a drive of the vehicle. There is no necessity that thedrive of the vehicle is prohibited, because of possible welding of thefirst contact and the second contact. This arrangement accordinglyenhances the convenience of the user while maintaining the sufficientsafety. The weld of the third contact is readily detected by setting apredetermined sequence to the on-off timings of the respective contactsand monitoring an inter-terminal voltage between terminals of thesecondary battery and an inter-power line voltage between the positiveand negative power lines of the direct voltage source.

In the third hybrid vehicle of the present invention, one preferablecontrol procedure measures both then inter-terminal voltage between theterminals of the secondary battery and the inter-power line voltagebetween the two power lines and stops a drive of the vehicle when it isdetermined that the observed inter-terminal voltage is equal to theobserved inter-power line voltage. This state suggests welding of thefirst contact or the second contact.

A diversity of structures are applicable to any of the first through thethird hybrid vehicles of the present invention and the hybrid vehiclesin the corresponding first through the third methods discussed above.Typical structures are a series hybrid vehicle and a parallel hybridvehicle. In one preferable example, the generator has a pair-rotorstructure including a pair of rotors rotatable relative to each otherand carries out power generation to attain a voltage and electric powercorresponding to a sliding rotational speed of the two rotors. Thisstructure corresponds to an electrical distribution type parallel hybridvehicle. There is also a mechanical distribution type parallel hybridvehicle. In this structure, the generator is linked with one shaft of athree-shaft power distributor, in which power input to and output fromone shaft is automatically determined when powers input to and outputfrom residual two shafts are specified. One example of the three-shaftpower distributor is a planetary gear mechanism. Another shaft of thethree-shaft power distributor is linked with an output shaft of theengine and still another shaft of the three-shaft power distributor islinked with the drive shaft of the vehicle. The parallel hybrid vehicleuses part of the power output from the engine as the driving force ofthe drive shaft. This desirably reduces the size of the motor in theparallel hybrid vehicle.

In one applicable structure for any of the first through the thirdhybrid vehicles and the corresponding first through third methods, thegenerator is connected to a first electric power driving circuit thatcauses the generator to carry out either one of a generative operationand a power operation, based on an on-off state of switching elementsincluded in the first electric power driving circuit, and the motor isconnected to a second electric power driving circuit that causes themotor to carry out either one of a power operation and a generativeoperation, based on an on-off state of switching elements included inthe second electric power driving circuit. This corresponds to thestructure of a semiconductor inverter and ensures accurate controlthrough regulation of the switching elements. Connection of the firstelectric power driving circuit with the second electric power drivingcircuit in this structure enables the hybrid vehicle to be driven in abattery-less drive mode that is free from the connection of the battery.It is, however, also practical to have a battery drive mode that isunder the connection of the battery. In the latter case, a secondarybattery or a high-capacity capacitor is connected to at least the firstelectric power driving circuit. Such connection enables the electricpower generated by the generator to be accumulated in the secondarybattery or the high-capacity capacitor.

In the structure that allows the hybrid vehicle to be driven in thebattery-less drive mode, one preferable embodiment provides a cutoffunit that cuts off connection between the secondary battery and thefirst electric power driving circuit. At least when a generative voltageby the generator is higher than an inter-terminal voltage betweenterminals of the secondary battery, the cutoff unit is actuated to cutoff the connection between the secondary battery and the first electricpower driving circuit. In the battery-less drive mode, when thesecondary battery has a low voltage level, part of the generatedelectric power may be used to charge the secondary battery. This reducesthe amount of electric power used for driving. The arrangement ofcutting off the connection between the secondary battery and the firstelectric power driving circuit by means of the cutoff unit enables allthe generated electric power to be used for driving the motor.

In the hybrid vehicle of the above structure, in response to detectionof a specific state that does not allow the secondary battery to becharged via the first electric power driving circuit, one preferableprocedure drives the motor with electric current that is induced by acounter electromotive force generated between terminals of themultiphase coil of the generator through the operation of the engine andruns via a rectifier arranged in combination with each switching elementin the first electric power driving circuit. Even in the case ofmalfunction of the switching element in the first electric power drivingcircuit, this arrangement assures power generation by the generator. Inthis structure, the generated electric power is autonomously determinedaccording to the loading. This significantly facilitates the drive ofthe hybrid vehicle in the battery-less drive mode.

These and other objects, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the preferred embodiments with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of a hybrid vehicle in one application ofthe present invention;

FIG. 2 schematically illustrates the general structure of a hybridvehicle in one embodiment of the present invention;

FIG. 3 shows connection of driving circuits with motors MG1 and MG2 inthe hybrid vehicle of FIG. 2;

FIG. 4A shows connection of an HV battery with system main relays SMR1,SMR2, and SMR3 in the hybrid vehicle of FIG. 2;

FIG. 4B shows a time sequence of on and off of relays SMR1,SMR2, andSMR3;

FIG. 5 is a block diagram illustrating the general configuration of acontrol system in the hybrid vehicle;

FIG. 6 is a flowchart showing a failure detection-time control routinefor battery-less drive executed in the embodiment;

FIG. 7 is a graph showing the target revolving speed NE* of an engineplotted against the vehicle speed SPD;

FIG. 8 is a graph showing an operation line OL in the mechanicaldistribution type hybrid vehicle;

FIG. 9 is a graph showing the counter electromotive force V plottedagainst the revolving speed Ng of the motor MG1 to describe the state ofpower generation utilizing the counter electromotive force;

FIG. 10 is a graph showing the amount of power generation P by the motorMG1 plotted against the revolving speed Ng of the motor MG1;

FIG. 11 shows a maximum generated output Pgmx at a predeterminedrevolving speed in the motor MG1;

FIG. 12 is a flowchart showing an essential part of a loading controlroutine executed by a master control CPU;

FIG. 13 shows a variation in motor torque Tm and a variation inrevolving speed NE of the engine;

FIG. 14 is a flowchart showing an essential part of a target revolvingspeed regulation routine executed by an engine ECU;

FIG. 15 is a flowchart showing a drive control routine for batter-lessdrive using inverters;

FIG. 16 is a graph showing a loss in the motor MG1;

FIG. 17 is a graph showing the torque Tg plotted against the revolvingspeed Ng of the motor MG1 with regard to the voltage Vm as a parameter;

FIG. 18 is a graph showing the relationship between the maximum outputtorque Temx and the revolving speed Ne of the engine;

FIG. 19 is a graph showing the required torque Td plotted against thevehicle speed with regard to the depression amount AP of the acceleratorpedal as a parameter;

FIG. 20 is a flowchart showing a drive control routine in the state of awelding failure of the system main relay SMR3;

FIG. 21 schematically illustrates the structure of a power output systemin an electrical distribution type hybrid vehicle; and

FIG. 22 shows a change of the drive mode in the hybrid vehicle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purpose of clarifying the configuration and the functions of thepresent invention, one mode of carrying out the present invention isdiscussed blow. FIG. 1 shows the configuration of a hybrid vehicle inone application of the present invention. An engine EG is an internalcombustion engine, in which gasoline is ejected from a fuel ejectionvalve IJ disposed in an intake port, taken into a cylinder SL by meansof the motion of a piston PT, compressed by the piston PT, and ignitedwith spark of a spark plug IP to be explosively combusted. The energy ofcombustion is taken out via the piston PT as rotating motions of acrankshaft CS. Driving conditions of the engine EG, especially theopening of a throttle valve TH and the quantity of fuel injection, areregulated by a specific engine control unit EFIECU. The engine controlunit EFIECU receives an observed revolving speed NE of the crankshaft CSmeasured by a speed sensor S1 and carries out feedback control with apredetermined gain G to make the observed revolving speed NE coincidentwith an externally given target revolving speed NE*.

A planetary gear unit PG is interposed between the crankshaft CS of theengine EG and a drive shaft DS of the vehicle. The planetary gear unitPG has three rotating shafts, which are respectively linked with thecrankshaft CS, a generator GN, and the drive shaft DS. A motor MG isalso disposed on the drive shaft DS. The torque transmitted from theengine EG via the planetary gear unit PG and the torque input into andoutput from the motor MG are transmitted to drive wheels via adifferential gear DF. A speed sensor S2 and a speed sensor S3 arerespectively attached to the generator GN and the drive shaft DS tomeasure the rotational speeds thereof.

Semiconductor inverters P1 and P2 are respectively connected to thegenerator GN and the motor MG as driving circuits. Controlling theon-off state of switching elements in the inverters P1 and P2 regulatesthe generated electric power by the generator GN and the power outputfrom the motor MG. Power lines of these two inverters P1 and P2 aremutually linked with each other. A battery BT is connected to the powerlines via a system main relay SMR. While the vehicle runs in a normalstate, the system main relay SMR is kept ON (that is, in the state ofconnection), and the electric power generated by the generator GN isaccumulated in the battery BT. The motor MG is driven by consuming theelectric power accumulated in the battery BT. In this configuration, themotor MG may be used as a generator, and the generator GN may be used asa motor.

A system controller SCNT controls the inverters P1 and P2 and the systemmain relay SMR. The system controller SCNT connects with the speedsensors S2 and S3, an accelerator pedal sensor APS that measures theamount of depression (the step-on amount) of an accelerator pedal AC, aremaining charge sensor RCS that measures a state of charge or remainingcharge SOC of the battery BT, and the inverters P1 and P2. The systemcontroller SCNT outputs the target revolving speed NE* of the engine EGto the engine control unit EFIECU.

During a normal run, the system controller SCNT calculates the power(revolving speed×torque) to be output to the drive shaft DS of thevehicle and the electric power to be generated by the generator GN,based on the observed amount of depression of the accelerator pedal AC,an observed revolving speed Nd of the drive shaft DS, and the observedstate of charge SOC of the battery BT. The system controller SCNT thencontrols the engine EG and the inverters P1 and P2 to attain the outputof the calculated power and the generation of the calculated electricpower. Whereas the engine control unit EFIECU controls the operations ofthe engine EG, the system controller SCNT outputs the target revolvingspeed NE* to indirectly regulate the output of the engine EG. Theprinciple of this regulation is described briefly.

The engine control unit EFIECU feedback controls the revolving speed ofthe engine EG. When there is a difference ΔN between the targetrevolving speed NE* and the actual revolving speed NE, the enginecontrol unit EFIECU regulates the quantity of air intake and thequantity of fuel injection and controls the power (revolvingspeed×torque) output from the engine EG, so as to make the actualrevolving speed NE coincident with the target revolving speed NE*. Inthe mechanical distribution type hybrid vehicle shown in FIG. 1, theplanetary gear unit PG is linked with the crankshaft CS. The generatorGN and the drive shaft DS are linked with the other shafts of theplanetary gear unit PG. The drive shaft DS is also connected to themotor MG. Controlling the generator GN and the motor MG forciblyregulates the revolving speed NE of the crankshaft CS. This arrangementenables the control that prevents the difference ΔN between the targetrevolving speed NE* and the actual revolving speed NE from beingimmediately reduced to zero even when the engine control unit EFIECUincreases the quantity of air intake and the quantity of fuel injection.When the difference ΔN is not reduced, the engine control unit EFIECUfurther regulates the quantity of air intake and the quantity of fuelinjection, so as to further increase or decrease the power possiblytaken out of the engine EG. The system controller SCNT specifies thetarget revolving speed NE* and regulates the rotational speeds of thegenerator GN and the motor MG. This regulates the revolving speed NE ofthe crankshaft CS and freely adjusts the energy taken out of the engineEG.

Based on the hardware structure and the principle of control discussedabove, the system controller SCNT shown in FIG. 1 carries out thefollowing control procedure in response to the occurrence of a failure.The system controller SCNT first detects a failure arising, for example,in the battery BT or the inverter P1 of the generator GN (step SA), andsets the inverter P1 and the system main relay SMR OFF in response todetection of the failure (step SB). The switch-off operation disconnectsthe battery BT from the circuit of the inverters P1 and P2. The systemcontroller SCNT then reads the revolving speeds of the respective shafts(step SC) and measures the amount of depression AP of the acceleratorpedal (step SD). The system controller SCNT subsequently changes therotational speed of the generator GN according to the required output ofthe vehicle calculated from the observed amount of depression AP and theresolving speed of the drive shaft DS (step SE), and controls the motorMG corresponding to the requirement of the vehicle (step SF).

In the state of the failure, the generator GN carries out powergeneration by utilizing the counter electromotive force of the generatorGN, instead of the general inverter-induced power generation. In thenormal state, the generator GN takes out the electric current induced byits coil, through which a magnetic field formed by permanent magnetspasses, thereby implementing the power generation. In the case ofmalfunction of the inverter P1, however, this general mechanism of powergeneration is not usable. Even when the inverter P1 is at a stop, themagnetic filed passing through the coil varies with the rotation of therotating shaft. A counter electromotive force is generated between bothends of the coil, in order to cancel the variation in magnetic field.When some load is connected to the power line, the counter electromotiveforce generated between both ends of the coil causes electric current tobe flown into the load via a protection diode arranged in combinationwith each switching element in the inverter P1. The generated output bythe generator GN in this state is determined autonomously according tothe magnitude of electric current flowing through the loading. Thegenerated output by utilizing the counter electromotive force isrestricted to be not greater than a predetermined value, whichcorresponds to a preset lower limit voltage, since the voltage decreaseswith an increase in output electric current. This predetermined value isspecified as a maximum generated power.

The above control procedure causes the vehicle to be driven in thefollowing manner. When the system controller SCNT reads a driver'srequirement from the amount of depression AP of the accelerator pedaland the revolving speed of the drive shaft DS and regulates the power(revolving speed×torque) output to the motor MG (step SF), the electricpower required by the motor MG is generated by utilizing the counterelectromotive force of the generator GN. The energy source of powergeneration by the generator GN is the engine EG. It is accordinglyrequired to control the output of the engine EG according to thevariation in generated electric power. This is attained by the feedbackcontrol of the revolving speed as discussed previously. The engine EG isunder the feedback control to the target revolving speed NE* by theengine control unit EFIECU. When the revolving speed NE of thecrankshaft CS is lowered, for example, due to an increase in generatedoutput by the generator GN or an increase in loading on the drive shaftDS of the vehicle, the engine control unit EFIECU increases the quantityof air intake and the quantity of fuel injection and raises the outputof the engine EG. At the same time, the rotational speed of thegenerator GN is varied according to the loading of the vehicle. Thegenerator GN is accordingly controlled with the engine EG as the energysource, in order to enable a greater power to be taken out correspondingto an increase in required power to be output to the drive shaft DS.

The above control procedure allows the continuous power generation bythe generator GN and enables the vehicle to be driven with the engine EGand the motor MG and safely reach a power station or any equivalentfacility even in the case of malfunction of the battery BT or theinverter P1. The above description regards the limp home drive mode inthe case of a malfunction. The technique of the present invention is,however, not restricted to the control procedure in the state of afailure but is applicable to any battery-less drive mode. Some modes ofcarrying out the present invention are discussed below as preferredembodiments.

The hybrid vehicle in one embodiment of the present invention isdiscussed below in the following sequence:

A. General Structure of Hybrid Vehicle

B. Basic Operations in Hybrid Vehicle

C. Configuration of Control System in Embodiment

D. Control by Engine ECU

E. Other Configuration

F. Control Procedure in Response to Detection of Failure

G. Battery-less Drive in Normal State of Inverters

H. Control Procedure in State of Welding Failure of System Main Relay

I. Structure of Electrical Distribution Type

J. Change of Drive Mode

A. General Structure of Hybrid Vehicle

FIG. 2 schematically illustrates the general structure of a hybridvehicle in one embodiment of the present invention. The hybrid vehiclehas three prime movers, that is, one engine 150 and two motor generatorsMG1 and MG2. Here the motor generator represents the prime moverfunctioning as both a motor and a generator. In the descriptionhereinafter, for simplicity of explanation, the motor generators aresimply referred to as the motors. The hybrid vehicle is under thecontrol of a control system 200.

The control system 200 includes a main ECU 210, a brake ECU 220, abattery ECU 230, and an engine ECU 240. Each of these ECUs isconstructed as an integral unit, where a plurality of circuit elementsincluding a microcomputer, an input interface, and an output interfaceare arranged on one identical circuit board. The main ECU 210 includes amotor controller 260 and a master controller 270. The master controller270 functions to determine a variety of control-relating quantities, forexample, distribution of the output from the three prime movers 150,MG1, and MG2.

The engine 150 is an ordinary gasoline engine that explosively combustsgasoline as fuel and rotates a crankshaft 156 with the combustionenergy. The engine ECU 240 controls operations of the engine 150. Theengine ECU 240 drives a throttle motor 152 to regulate the opening θ ofa throttle valve 151 disposed in an air intake pipe and actuates a fuelinjection valve 154 to regulate the quantity of fuel injection τ intothe engine 150, based on the target revolving speed NE* directed by themaster controller 270.

The motors MG1 and MG2 are constructed as synchronous motors, andrespectively include rotors 132 and 142 with a plurality of permanentmagnets mounted on outer circumferences thereof, and stators 133 and 143with three-phase coils 131 and 141 wound thereon to form revolvingmagnetic fields. The stators 133 and 142 are fixed to a casing 119. Thethree-phase coils 131 and 141 wound on the stators 133 and 143 of themotors MG1, and MG2 are respectively connected to a secondary battery orhigh voltage (HV) battery 194 via driving circuits 191 and 192. FIG. 3shows in detail the connection of the driving circuits 191 and 192 withthe motors MG1 and MG2. The driving circuits 191 and 192 are constructedas transistor inverters that respectively include transistors Tr1through Tr6 and Tr11 through Tr16, which are arranged in pairs for therespective phases, between power lines L1 and L2 connected to the HVbattery 194 via a system main relay SMR. A capacitor C is interposedbetween the power lines L1 and L2 to relieve a voltage variation. Aprotection diode D is in inverse contact between a collector and anemitter of each of the switching elements Tr1 through Tr6 and Tr11through Tr16.

The driving circuits 191 and 192 are controlled by the motor controller260. The driving circuit 191 has current sensors 181 and 182 thatrespectively measure the U-phase electric current and the V-phaseelectric current, whereas the driving circuit 192 has similar currentsensors 185 and 186. Observed values of electric current Iu1, Iv1, Iu2,and Iv2 are input into the motor controller 260. The motor controller260 receives the observed phase currents and outputs control signals Sw1and Sw2 to attain the desired power output. The transistors included inthe driving circuits 191 and 192 are switched on and off, in response tothe output control signals Sw1 and Sw2. The electric current flowsbetween the battery 194 and the motors MG1 and MG2 via the transistorsin the ON state. Each of the motors MG1 and MG2 may function as themotor that receives a supply of electric power from the HV battery 194to be driven and rotated (hereinafter this state of operation isreferred to as the power operation). While the rotor 132 or 142 isrotated by an external force, the motor MG1 or MG2 may function as thegenerator that causes an electromotive force to be generated betweenboth ends of the three-phase coil 131 or 141 and charges the HV battery194 (hereinafter this state of operation is referred to as the powergeneration or regenerative operation). Even when the switching elementsare not switched on, the rotation of the rotor in the motor causes themagnetic field formed by the permanent magnets to pass through thethree-phase coil. This varies the magnetic flux passing through thethree-phase coil and generates a counter electromotive force in eachphase coil. The counter electromotive force simply raises theinter-terminal voltage without any loading. When a load is connectedbetween the power lines L1 and L2, however, the electric current runsvia the protection diode D arranged in combination with each switchingelement. This enables the motor MG1 or the motor MG2 to carry out powergeneration. The power generation by utilizing the counter electromotiveforce will be discussed in detail later.

The HV battery 194 and the motors MG1 and MG2 are also connected to anauxiliary machinery battery 198 via a converter 252. This arrangementenables the high voltage electrical energy generated by the motors MG1and MG2 or accumulated in the HV battery 194 to be converted into a lowvoltage of DC 12[V] and charges the auxiliary machinery battery 198 withthe converted low voltage electrical energy.

FIG. 4A shows in detail the connection of the HV battery 194 with thesystem main relay SMR. The HV battery 194 is divided into two batterygroups in the structure. The two battery groups are connected with eachother via a high voltage fuse HF and a service plug SP. The service plugSP is provided to cut off the high voltage system for inspection,maintenance, and other purposes. Two system main relays SMR1 and SMR2are provided in the positive power line L1 of the HV battery 194. Theelement actually included in the circuit is naturally the contact ofeach relay. For convenience of explanation, here the contact is calledthe system main relay SMR. The system main relay SMR1 in combinationwith a current restriction resistor R for restricting the electriccurrent forms a bypass circuit, relative to the system main relay SMR2.A system main relays SMR3 is provided in the negative power line L2 ofthe HV battery 194.

At the time of power supply of the high voltage system, the three systemmain relays SMR1, SMR2, and SMR3 are controlled according to thefollowing procedure. In order to start the operation of the vehicle, theprocedure first switches the system main relay SMR3 ON (in the closedstate) and then, after elapse of a preset time T1, the system main relaySMR1 ON. The system main relays SMR2 is switched ON after elapse ofanother preset time T2. When the system main relay SMR1 is closed asshown in FIG. 4B, the electric current starts flowing via the currentrestriction resistor R to restrict the magnitude of rush current. Thisarrangement effectively prevents the contact of the system main relaySMR1 from being welded by the arc of large electric current. Since theelectric current has already flown via the current restriction resistorR, the system main relay SMR2 in the closed state is protected fromwelding. At the time of cutting off the high voltage power source, asshown in FIG. 4B, the procedure first switches the system main relaySMR2 OFF (in the open state) and then, after elapse of a preset time T3,the system main relay SMR3 OFF. The system main relay SMR1 is switchedOFF after elapse of another preset time T4.

The system main relays SMR1, SMR2, and SMR3 are switched on and switchedoff in different sequences at the time of power supply and at the timeof power cut off as described above. An HV battery sensor 196 measuresan output voltage Vbt of the HV battery 194, whereas a voltage sensor197 measures a voltage Vhv of the power line. The welding failure ofeach system main relay SMR is detected according to the on-off state ofthe system main relays SMR and the relation of the voltages Vbt and Vhv.In the course of power supply, if Vbt=Vhv when the system main relaySMR3 is switched ON, the procedure determines that either the systemmain relay SMR1 or the system main relay SMR2 welds. In the course ofpower cut off, if Vbt=Vhv when the system main relay SMR1 is switchedOFF, the procedure determines that the system main relay SMR3 welds. Adiversity of methods are applicable to diagnose the welding failure. Forexample, one applicable method detects the welding failure by switchingon and off the respective contacts in different sequences. Anothermethod disposes a current sensor in a circuit passing through eachcontact.

Referring back to FIG. 2, the power output system from the engine 150 tothe drive shaft is described. The rotating shafts of the engine 150 andthe motors MG1 and MG2 are mechanically linked with one another via aplanetary gear 120. The planetary gear 120 includes a sun gear 121, aring gear 122, and a planetary carrier 124 with a planetary pinion gearl23. In the hybrid vehicle of the embodiment, the crankshaft 156 of theengine 150 is coupled with a planetary carrier shaft 127 via a damper130. The damper 130 is provided to absorb torsional vibrations arisingon the crankshaft 156. The rotor 132 of the motor MG1 is linked with asun gear shaft 125, whereas the rotor 142 of the motor MG2 is linkedwith a ring gear shaft 126. The rotation of the ring gear 122 istransmitted to an axle 112 and wheels 116R and 116L via a chain belt 129and a differential gear 114.

The control system 200 utilizes a diversity of sensors to attain thecontrol of the whole hybrid vehicle. Such sensors include an acceleratorsensor 165 that measures the amount of depression or step-on amount ofan accelerator pedal by a driver, a gearshift position sensor 167 thatdetects the position of a gearshift lever, a brake sensor 163 thatmeasures the step-on pressure of a brake pedal, a battery sensor 196that measures the charge level or state of charge (SOC) of the HVbattery 194, and a speed sensor 144 that measures the revolving speed ofthe motor MG2. The ring gear shaft 126 is mechanically linked with theaxle 112 via the chain belt 129, so that the ratio of the revolvingspeeds of the ring gear shaft 126 to the axle 112 is fixed. The speedsensor 144 disposed on the ring gear shaft 126 accordingly detects therevolving speed of the axle 112 as well as the revolving speed of themotor MG2.

B. Basic Operations in Hybrid Vehicle

The description first regards the operations of the planetary gear 120to explain the basic operations in the hybrid vehicle. In the planetarygear 120, when the revolving speeds of any two rotating shafts among thethree rotating shafts mentioned above are specified, the revolving speedof the residual rotating shaft is automatically determined. Therevolving speeds of the respective rotating shafts hold the relationshipdefined as Equation (1) given below:

Nc=Ns×ρ/(1ρ)+Nr×1/(1+ρ)  (1)

where Nc, Ns, and Nr respectively denote the revolving speed of theplanetary carrier shaft 127, the revolving speed of the sun gear shaft125, and the revolving speed of the ring gear shaft 126, and ρrepresents the gear ratio of the sun gear 121 to the ring gear 122 asexpressed by the following equation:

ρ=[number of teeth of sun gear 121]/[number of teeth of ring gear 122]

The torques of the three rotating shafts hold fixed relations defined asEquations (2) and (3) given below, irrespective of their revolvingspeeds:

Ts=Tc×ρ/(1+ρ)  (2)

Tr=Tc×1/(1+ρ)=Ts/ρ  (3)

where Tc, Ts, and Tr respectively denote the torque of the planetarycarrier shaft 127, the torque of the sun gear shaft 125, and the torqueof the ring gear shaft 126.

The functions of the planetary gear 120 enable the hybrid vehicle of theembodiment to run in a variety of conditions. For example, in the stateof a drive at a relatively low speed immediately after the start of thehybrid vehicle, the motor MG2 carries out the power operation totransmit the power to the axle 112 and drive the hybrid vehicle, whilethe engine 150 is at a stop or at an idle.

When the speed of the hybrid vehicle reaches a predetermined level, thecontrol system 200 causes the motor MG1 to carry out the power operationand motors and starts the engine 150 with the torque output through thepower operation of the motor MG1. At this moment, the reactive torque ofthe motor MG1 is output to the ring gear 122 via the planetary gear 120.

When the engine 150 is driven to rotate the planetary carrier shaft 127,the sun gear shaft 125 and the ring gear shaft 126 rotate under theconditions fulfilling Equations (1) through (3) given above. The powergenerated by the rotation of the ring gear shaft 126 is directlytransmitted to the wheels 116R and 116L. The power generated by therotation of the sun gear shaft 125 is, on the other hand, regenerated aselectric power by the first motor MG1. The power operation of the secondmotor MG2 enables the power to be output to the wheels 116R and 116L viathe ring gear shaft 126.

In the state of a stationary drive, the output of the engine 150 is setsubstantially equal to a required power of the axle 112 (that is, therevolving speed×torque of the axle 112). In this state, part of theoutput of the engine 150 is transmitted directly to the axle 112 via thering gear shaft 126, while the residual power is regenerated as electricpower by the first motor MG1. The second motor MG2 utilizes theregenerated electric power to produce a torque for rotating the ringgear shaft 126. The axle 112 is accordingly driven at a desiredrevolving speed and a desired torque. The control operation of theengine 150 in the stationary driving state will be discussed later.

When there is an insufficiency of the torque transmitted to the axle112, the second motor MG2 supplements the insufficient torque. Theelectric power obtained by the regenerative operation of the first motorMG1 and the electric power accumulated in the HV battery 194 are usedfor such supplement. In this manner, the control system 200 controls theoperations of the two motors MG1 and MG2 according to the required powerto be output from the axle 112.

The hybrid vehicle of the embodiment may go back in the active state ofthe engine 150. While the engine 150 is driven, the planetary carriershaft 127 rotates in the same direction as that in the case of theforward drive. In this state, when the first motor MG1 is controlled torotate the sun gear shaft 125 at a higher revolving speed than therevolving speed of the planetary carrier shaft 127, the rotatingdirection of the ring gear shaft 126 is inverted to the direction forthe rearward drive as clearly understood from Equation (1) given above.The control system 200 makes the second motor MG2 rotated in thedirection for the rearward drive and regulates the output torque, thusenabling the hybrid vehicle to go back.

In the planetary gear 120, the planetary carrier 124 and the sun gear121 may be rotated while the ring gear 122 is at a stop. The engine 150is accordingly driven while the vehicle is at a stop. For example, whenthe HV battery 194 has a low charge level, the engine 150 is driven andcauses the first motor MG1 to carry out the regenerative operation andcharge the HV battery 194. The power operation of the first motor MG1 inthe stationary state of the vehicle, on the other hand, motors andstarts the engine 150 with the output torque.

C. Configuration of Control System in Embodiment

FIG. 5 is a block diagram illustrating the detailed configuration of thecontrol system 200 in this embodiment. The master controller 270includes a master control CPU 272 and a power source control circuit274. The motor controller 260 includes a main motor control CPU 262 andtwo motor control CPUs 264 and 266 that respectively control the twomotors MG1 and MG2. Each of the CPUs is constructed as a one-chipmicrocomputer including a CPU, a ROM, a RAM, an input port, and anoutput port (not shown).

The master control CPU 272 functions to determine the control-relatingquantities, for example, the distribution of the revolving speeds andthe torques of the three prime movers 150, MG1, and MG2 and transmit adiversity of required values to the other CPUs and ECUs, so as tocontrol the operations of the respective prime movers. In order toattain such control, accelerator position signals AP1 and AP2representing the accelerator position or opening, gearshift positionsignals SP1 and SP2 representing the gearshift position, and theignition signal IG that represents an ignition-related operation and istransmitted from the ignition sensor 169 are directly connected to aninput port of the master control CPU 272. The master control CPU 272also receives a brake signal BP transmitted from the brake sensor 163via the brake ECU 220. Both the accelerator sensor 165 and the gearshiftposition sensor 167 have a dual structure, that is, include two sensorelements. The master control CPU 272 accordingly receives the twoaccelerator position signals AP1 and AP2 and the two gearshift positionsignals SP1 and SP2. The master control CPU 272 also controls the on-offstate of the system main relays SMR to connect and cut off the highvoltage power source from the HV battery 194 as discussed above. For thepurpose of such on-off control, the master control CPU 272 monitors thestate of the ignition sensor 169 that detects a turning motion of anignition key. Indicators and lamps provided on an inner panel areconnected to an output port of the master control CPU 272. In theillustration of FIG. 5, only a diagnosis lamp 291 is shown as a typicalexample. The master control CPU 272 controls its output port to directlylight these indicators and lamps.

As illustrated in FIG. 5, the master control CPU 272 is connected withthe converter 252 that converts the high voltage direct current of theHV battery 194 into low voltage direct current and with a voltage sensor199 that is mounted on the auxiliary machinery battery 198 to measurethe voltage of the auxiliary machinery battery 198 and output ameasurement signal VCE. The ignition sensor 169 outputs the startingrequirement signal IG in response to a turning motion of the ignitionkey. The starting requirement signal IG switches the relay 197 on toallow supply of the low voltage power source Vcc. The master control CPU272 receives the supply of the low voltage power source Vcc, switches onand off the system main relays SMR according to the voltage VCE of theauxiliary machinery battery 198, and controls the operations of theconverter 252 when required. The power source control circuit 274incorporated in the master controller 270 has the function of amonitoring circuit that monitors abnormality in the master control CPU272.

The main motor control CPU 262 transmits required electric currentsI1req and I2req to the two motor control CPUs 264 and 266, based onrequired torques T1req and T2req of the two motors MG1 and MG2 given bythe master control CPU 272. The motor control CPUs 264 and 266respectively output the control signals Sw1 and Sw2 according to therequired electric currents I1req and I2req, so as to control the drivingcircuits 191 and 192 and drive the motors MG1 and MG2. The speed sensorsof the motors MG1 and MG2 feed revolving speeds REV1 and REV2 of themotors MG1 and MG2 back to the main motor control CPU 262. The mastercontrol CPU 272 receives the revolving speeds REV1 and REV2 of themotors MG1 and MG2 as well as a value of electric current IB suppliedfrom the HV battery 194 to the driving circuits 191 and 192, which arefed back from the main motor control CPU 262.

The battery ECU 230 monitors the state of charge or charge level SOC ofthe HV battery 194 and supplies a required value of charging CHreq ofthe HV battery 194, when required, to the master control CPU 272. Themaster control CPU 272 determines the output of each prime mover bytaking into account the required value of charging CHreq. In the case ofa requirement for charging, the master control CPU 272 causes the engine150 to output a greater power than the value required for the drive anddistributes part of the output power to the charging operation by meansof the first motor MG1.

The brake ECU 220 carries out control to balance a hydraulic brake (notshown) with the regenerative brake by the second motor MG2. This isbecause the second motor MG2 carries out the regenerative operation tocharge the HV battery 194 in the course of braking the hybrid vehicle ofthe embodiment. In accordance with a concrete procedure, the brake ECU220 transmits a required regenerative power REGreq to the master controlCPU 272, based on the brake pressure BP measured by the brake sensor163. The master control CPU 272 specifies the operations of the motorsMG1 and MG2 in response to the required regenerative power REGreq andfeeds an actual regenerative power REGprac back to the brake ECU 220.The brake ECU 220 regulates the amount of braking by the hydraulic braketo an adequate value, based on the observed brake pressure BP and thedifference between the required regenerative power REGreq and the actualregenerative power REGprac.

D. Control by Engine ECU

The engine ECU 240 controls the engine 150 according to the targetrevolving speed NE* transmitted from the master control CPU 272 asdiscussed below. The engine ECU 240 basically carries out the feedbackcontrol of the revolving speed. The master control CPU 272 specifies thetarget revolving speed NE*. The engine ECU 240 obtains the actualrevolving speed NE of the engine 150 and calculates the difference ΔNbetween the actual revolving speed NE and the target revolving speedNE*. When the actual revolving speed NE is lower than the targetrevolving speed NE*, the engine ECU 240 controls the throttle motor 152to widen the opening θ of the throttle valve 151. The engine ECU 240also controls the air fuel ratio. When the throttle valve 151 is open toincrease the quantity of air intake, the quantity of fuel injection τincreases accordingly. The procedure of feedback control carries out thePID control with a high gain G1 in a range of significantly largedifference ΔN between the actual revolving speed NE and the targetrevolving speed NE*. When the difference ΔN decreases to be within apredetermined range ±E1, the control procedure changes the gain to avalue G2 that is lower than G1. When the difference ΔN further decreasesto enter a very narrow range ±E2 (E2<E1), the control procedure variesthe gain by a predetermined skipping value, in order to make therevolving speed difference ΔN kept in this narrow range ±E2. Even in thecontrol system where the response has a time lag of first order as inthe case of the engine 150, this arrangement ensures the stability ofcontrol and makes the actual revolving speed coincident with the targetrevolving speed.

The throttle opening θ is anyway widened with an increase in differenceΔN. The hybrid vehicle of the embodiment regulates the difference ΔN, soas to adjust the output (revolving speed×torque) from the engine 150. Inorder to enhance the output from the engine 150, the hybrid vehiclecarries out the control to cause the difference ΔN between the targetrevolving speed NE* and the actual revolving speed NE. The control mayraise the target revolving speed NE* or regulate the rotational speedsof the motors MG1 and MG2 connected to each other via the planetary gear120 according to Equation (1) given above, so as to forcibly lower therevolving speed of the crankshaft 156.

Under the condition that the feedback control has caused the engine 150to be driven at the target revolving speed NE* (the difference ΔN=0), adecrease in reactive torque applied to the crankshaft 156 immediatelyraises the revolving speed NE of the engine 150. The decrease inreactive toque is caused, for example, by decreasing the amount ofdepression AP of the accelerator pedal or by lowering the load of thedrive shaft according to the configuration of the ground, for example, achange from an ascent to a descent. The raised revolving speed NE causesthe revolving speed difference ΔN. The engine ECU 240 narrows theopening θ of the throttle valve 151 and decreases the output of theengine 150, in order to cancel the difference ΔN. When the revolvingspeed of the engine 150 is lowered by the increased loading, on thecontrary, there is also the revolving speed difference ΔN. The engineECU 240 widens the opening θ of the throttle valve 151 and immediatelyincreases the output of the engine 150, in order to cancel thedifference ΔN. The output of the engine 150 is also variable by varyingthe target revolving speed NE*.

As described above, while the engine ECU 240 feedback controls therevolving speed of the engine 150, the master controller 270 sets theconditions to cause the revolving speed difference ΔN, so as to enable adesired power to be taken out of the engine 150. Even in the case of anabrupt variation in loading, this control procedure does not requireupdating the target output given to the engine 150. The engine ECU 240transmits the actual revolving speed NE of the engine 150 to the mastercontrol CPU 272, so that the master control CPU 272 is always informedof the actual revolving speed NE of the engine 150.

E. Other Configuration

As described above, the master control CPU 272 determines the targetrevolving speed of the engine 150 and the outputs of the motors MG1 andMG2 and transmits the required values to the ECU 240 and the CPUs 264and 266, which take in charge of the actual controls. The ECU 240 andthe CPUs 264 and 266 control the corresponding prime movers in responseto the required values. The hybrid vehicle is accordingly driven withthe adequate power output from the axle 112 according to the drivingstate. In the course of braking, the brake ECU 220 cooperates with themaster control CPU 272 to regulate the operations of the respectiveprime movers and the hydraulic brake. This arrangement attains thedesirable braking operation that does not make the driver uneasy oruncomfortable, while allowing regeneration of electric power.

The two control CPUs 262 and 272 are connected to an abnormality recordregistration circuit 280 via bidirectional communication lines 214 and216 to read and write data. There is another bidirectional communicationline 212 interposed between the master control CPU 272 and the mainmotor control CPU 262 to transmit a variety of data includingverification of the validity of the processing.

An input port of the abnormality record registration circuit 280receives reset signals RES1 and RES2 transmitted between the mastercontrol CPU 272 and the main motor control CPU 262. The abnormalityrecord registration circuit 280 registers the input reset signals RES1and RES2 into an internal EEPROM 282. Namely the abnormality recordregistration circuit 280 has the function of monitoring generation ofthe reset signal and registering the generation record in response to areset of the master control CPU 272 or the main motor control CPU 262.

F. Control Procedure in Response to Detection of Failure

The following describes the control procedure carried out when anyabnormality arises in the HV battery 194 or the driving circuit 191. Asdescribed previously, when there is a failure in the HV battery 194 orin the driving circuit 191 to interfere with the normal on-off operationof the transistors Tr functioning as the switching elements, the controlprocedure sets the system main relay SMR OFF and enables the vehicle tobe driven in the battery-less drive mode. In such cases, the motor MG1functions as the generator utilizing the counter electromotive force.The failure of the HV battery 194 is identified, for example, when thestate of charge or remaining charge SOC obtained from the observedvoltage by the HV battery sensor 196 is not varied by the charging anddischarging control via the driving circuit 191 or when an abnormaltemperature level is detected by a temperature sensor (not sown). Thefailure of the switching elements in the driving circuit 191 isidentified, based on the measurements of the current sensors 181 and182.

FIG. 6 is a flowchart showing a failure detection-time control routineexecuted in the embodiment. This control routine is activated at thetime of detection of a failure and carried out after the system mainrelay SMR is set OFF. The system main relay SMR is set OFF at the timeof detection of the failure, since the power generation of the motor MG1by utilizing the counter electromotive force generally lowers theinter-power line voltage between the power lines L1 and L2 of thedriving circuit 191 below the inter-terminal voltage of the HV battery194. When the comparison between the inter-power line voltage and theinter-terminal voltage shows that the inter-terminal voltage of the HVbattery 194 is low, the control procedure may not set the system mainrelay SMR OFF.

When the program enters the control routine shown in the flowchart ofFIG. 6, the procedure first reads the current vehicle speed SPD, theamount of depression AP of the accelerator pedal, and the revolvingspeed Nd of the drive shaft (that is, the axle) at step S100, anddetermines the target revolving speed NE* of the engine 150 based onthese inputs at step S110. The concrete process of step S110 reads thetarget revolving speed NE* of the engine 150 from a map provided forcontrol in the state of failure as shown in FIG. 7. In the map of FIG. 7used in this embodiment, the target revolving speed NE* of the engine150 increases with an increase in vehicle speed SPD. The solid curve ofFIG. 7 represents the base characteristic without taking into accountthe amount of depression AP of the accelerator pedal. In the actualstate, however, the target revolving speed NE* is varied according tothe amount of depression AP of the accelerator pedal. In a low vehiclespeed range, the target revolving speed NE* is raised with an increasein amount of depression AP of the accelerator pedal. This low vehiclespeed range is shown as a hatched area ORA in FIG. 7. In a concreteexample, when the driver depresses the accelerator pedal to the fullopen position, the target revolving speed NE* is set higher by 700 rpmthan the base value. When the accelerator pedal is depressed to the halfopen position, the target revolving speed NE* is set higher by 300 rpmthan the base value. The curve of broken line GD in FIG. 7 representsthe characteristic of the target revolving speed NE* under the conditionthat the accelerator pedal is depressed to the full open position.

Another procedure may set the engine speed NE* by taking into accountthe differential of the depression amount AP of the accelerator pedal.When the driver depresses the accelerator pedal, this procedure raisesthe target revolving speed NE* in advance while the vehicle speed SPD isstill low. Namely this procedure raises the target revolving speed NE*to be higher than the level set in stationary state according to the mapof the target revolving speed NE* against the vehicle speed SPB and thedepression amount AP of the accelerator pedal. This method effectivelyensures the future output of the engine 150 that will be required in ashort time period.

The revolving speed Nd of the axle or drive shaft, the revolving speedNE of the engine 150, and the revolving speed Ng of the motor MG1 hold arelationship following Equation (1) given above. Namely there is therelationship of:

NE=Ng×ρ/(1+ρ)+Nd×1/(1+ρ)  (1a)

The revolving speed Nd of the axle is obtained unequivocally from thevehicle speed SPD. Setting the revolving speed NE of the engine 150 thusunequivocally determines the revolving speed Ng of the motor MG1. Thisrelationship is shown in the map of FIG. 8. The three revolving speedsNd, NE, and Ng always form a straight line (operation line OL). Therevolving speed of the motor MG1 is thus adjusted by regulating therevolving speed NE of the engine 150. There is a time lag in the controlof the engine 150. Setting the target revolving speed NE* does notimmediately make the actual revolving speed of the motor MG1 coincidentwith the calculated revolving speed. The procedure then reads therevolving speed Ng of the motor MG1 at step S120.

In the arrangement of the embodiment, the revolving speed Ng of themotor MG1 functioning as the generator is varied according to thevehicle speed SPD and the depression amount AP of the accelerator pedal.This is because a maximum generated output Pgmx, which is taken out ofthe motor MG1 functioning as the generator by the power generationutilizing the counter electromotive force, depends upon the revolvingspeed Ng of the motor MG1. The procedure determines the maximumgenerated output Pgmx of the motor MG1 at step S130.

The process of determining the maximum generated output Pgmx isdescribed in detail. In the case of the power generation by utilizingthe counter electromotive force, as shown by the characteristic curvesof non-loading power generation NL and maximum power generation LD inFIG. 9, the voltage V of power generation increases with an increase inrevolving speed Ng of the motor MG1. The generated output P increaseswith an increase in revolving speed Ng as shown in FIG. 10. Under thecondition of a fixed revolving speed Ng, the voltage V of powergeneration decreases with an increase in generated output P as shown inFIG. 11. When the generated output P exceeds a predetermined value Pgmx,the voltage V abruptly decreases. The voltage V of power generationlower than a preset value does not allow the converter 252 to beactuated. The procedure of the embodiment thus sets the upper limit ofpower generation that ensures the voltage V of power generation to benot less than 150 V, as the maximum generated output Pgmx. The graph ofFIG. 11 shows the characteristic curve when the revolving speed Ng ofthe motor MG1 is equal to 6000 rpm. In this case, the maximum generatedoutput Pgmx is approximately equal to 4 kw.

The procedure inputs the revolving speed Ng of the motor MG1 at stepS120 and reads the maximum generated output Pgmx corresponding to theinput revolving speed Ng from the map stored in advance at step S130.The procedure subsequently calculates a required torque Td of the axlefrom the observed vehicle speed SPD and the depression amount AP of theaccelerator pedal at step S140 and determines an output torque Tm of themotor MG2 to attain the required torque Td at step S150. The procedurethen calculates an amount of power consumption Pm at step S160 andregulates the output torque Tm to restrict the calculated amount ofpower consumption Pm to the maximum generated output Pgmx at step S170.The procedure subsequently controls the on-off state of the switchingelements or transistors Tr11 through Tr16 in the driving circuit 192 andcauses the motor MG2 to carryout the power operation with the torque Tmat step S180.

The power generation utilizing the counter electromotive force does notcarry out the on-off control of the transistors in the first drivingcircuit 191. As long as no load is connected between the terminals ofthe motor MG1, when the rotor with the permanent magnets attachedthereto rotates to vary the density of magnetic flux passing through thethree-phase coil 131, the counter electromotive force is generatedbetween the terminals to cancel the variation in density of the magneticflux. As shown in FIG. 3, when the counter electromotive force isgenerated between the terminals of each phase coil in the motor MG1 anda load is connected between the power lines L1 and L2, the electriccurrent runs via the protection diode connected between the collectorand the emitter of each of the transistors Tr1 through Tr6. Themagnitude of the electric current depends upon the magnitude of theloading. Namely the power generation utilizing the counter electromotiveforce automatically generates the electric power corresponding to theelectric power consumed by the loading within the range of the maximumgenerated output Pgmx. In the arrangement of the embodiment, themagnitude of the loading is adjusted by regulating the ON time of thetransistors Tr11 through Tr16 for the power operation of the MG2.

When there is any failure in the HV battery 194 or in the first drivingcircuit 191, the arrangement of the embodiment sets the system mainrelay SMR OFF and enables the vehicle to be driven in the battery-lessdrive mode. In the battery-less drive mode, the engine 150 is driven andthe motor MG1 is used as the generator utilizing the counterelectromotive force. This ensures the power of several kilowatts. In thecase of the limp home drive in the state of failure, this arrangementensures a certain level of vehicle speed and a driving distancedetermined by the remaining quantity of fuel (gasoline) in the vehicle.For example, when some abnormality arises in the vehicle during a driveon an express way, this arrangement enables the vehicle to be driven atthe certain level of vehicle speed and thereby ensures the safety of thedrive.

The procedure of the embodiment varies the target revolving speed NE* ofthe engine 150 according to the required power of the vehicle andaccordingly regulates the revolving speed Ng of the motor MG1functioning as the generator, so as to adjust the maximum generatedoutput Pgmx in the power generation utilizing the counter electromotiveforce. This arrangement effectively prevents the engine 150 from beingcontinuously driven in a high speed range and overheated. The revolvingspeeds of the engine 150 and the motor MG1 vary according to the outputof the vehicle. This advantageously makes the driver feel compatibilityduring a drive of the vehicle.

The arrangement of the embodiment discussed above may be subjected tosome modification. In the structure of the embodiment, the engine ECU240 carries out the feedback control of the revolving speed of theengine 150, and the master control CPU 272 transmits the targetrevolving speed NE* to the engine ECU 240 through communication. In onemodified structure discussed below, there is no communication betweenthe master control CPU 272 and the engine ECU 240. In this example, theengine ECU 240 independently regulates the target revolving speed NE* ofthe engine 150. One example of the processing carried out in thismodified structure is shown in the flowcharts of FIGS. 12 and 14. Theflowchart of FIG. 12 shows a control routine executed by the mastercontrol CPU 272, and the flowchart of FIG. 14 shows a control routineexecuted by the engine ECU 240.

When the master control CPU 272 determines at step S200, based on thedriving conditions of the vehicle, that an increase in revolving speedof the engine 150 is required, the master control CPU 272 increases theoutput torque Tm of the motor MG2 in a short time period at step S210.This process increases the electric current flowing through the motorMG2 and thereby enhances the loading torque of the motor MG1 functioningas the generator. The loading torque is applied to the engine 150, sothat the revolving speed NE of the engine 150 is temporarily lowered ata timing tp1 shown in the graph of FIG. 13. When the master control CPU272 determines at step S200, based on the driving conditions of thevehicle, that a decrease in revolving speed of the engine 150 isrequired, on the other hand, the master control CPU 272 decreases theoutput torque Tm of the motor MG2 in a short time period at step S220.This process decreases the electric current flowing through the motorMG2 and thereby reduces the loading torque of the motor MG1 functioningas the generator. The revolving speed NE of the engine 150 is thustemporarily heightened at a timing tp2 shown in the graph of FIG. 13.

Referring to the flowchart of FIG. 14, the engine ECU 240 continuouslymonitors the revolving speed of the engine 150 at step S300. When theactual revolving speed NE of the engine 150 coincides with the targetrevolving speed NE* at step S305, the engine ECU 240 carries out theseries of processing discussed below. The engine ECU 240 compares avariation ΔNN in revolving speed NE per unit time with a predeterminedrange ±ΔNref at step S310. When ΔNN<−ΔNref, the engine ECU 240increments the target revolving speed NE* by a preset value N1 from thecurrent level at step S320. When ΔNN>ΔNref, on the other hand, theengine ECU 240 decrements the target revolving speed NE* by the presetvalue N1 from the current level at step S330. In the case where thevariation ΔNN in revolving speed NE is within the predetermined range±ΔNref, the engine ECU 240 does not change the target revolving speedNE* of the engine 150 but keeps the current level.

While the master control CPU 272 and the engine ECU 240 do not transmitdata, the above control procedure enables the master control CPU 272 tovary the revolving speed of the engine 150. In the structure that allowscommunication between the master control CPU 272 and the engine ECU 240,even when there is a failure in the communication system, thisarrangement enables the revolving speed of the engine 150 to approach adesired level and exerts the effects of the embodiment discussed above.This arrangement regulates the output of the engine according to therequired torque of the vehicle and enables the vehicle to be driven withthe required torque.

The above procedure regulates the target revolving speed NE* in responseto a variation in actual revolving speed NE of the engine 150. Inanother modified arrangement, the engine ECU 240 directly detects thebehavior of the accelerator pedal, that is, the variation in depressionamount AP of the accelerator pedal (the operation in the openingdirection or the operation in the closing direction). The engine ECU 240regulates the target revolving speed NE* based on the detected behaviorof the accelerator pedal.

G. Battery-less Drive in Normal State of Inverters

The arrangement of the above embodiment causes the vehicle to be drivenin the battery-less drive mode in which the power generation is carriedout by utilizing the counter electromotive force on the assumption thatthere is a failure in the HV battery 194 or another related element. Thevehicle may alternatively be driven in another type of battery-lessdrive mode in which the power generation does not utilize the counterelectromotive force but uses the driving circuits 191 and 192functioning as the inverters. The vehicle may be driven in this type ofbattery-less drive mode in the normal state or in an abnormal state witha failure in the HV battery 194 while there is no abnormality in thedriving circuits 191 and 192 functioning as the inverters. When there isan abnormality only in the HV battery 194, the battery-less driveseparating the HV battery 194 advantageously ensures a drive of the highpower performance. The battery-less drive still exerts some advantagesin the normal state where the HV battery 194 and the driving circuits191 and 192 are all normal. The drive of the vehicle in the state thatthe amount of power generation completely balances with the amount ofpower consumption does not require either charging or discharging the HVbattery 194, thus desirably extending the life of the HV battery 194. Inthe case where the HV battery 194 has an excessively high temperaturethrough the charging or discharging process, the battery-less drive withthe HV battery 194 temporarily separated favorably gives the time ofcooling does the HV battery 194.

In the case of the battery-less drive in the normal state, it isrequired to make the amount of power generation by the motor MG1 balancewith the amount of power consumption by the motor MG2. This is attainedby the series of processes discussed below:

(1) Calculation of required output of power generation Pgr: The processspecifies the current amount of power consumption by the motor MG2including a loss of the system, so as to calculate a required output ofpower generation Pgr, which represents the amount of electric power tobe generated by the motor MG1 functioning as the generator.

(2) Calculation of target torque Tgi: The process calculates a targettorque Tgi of the motor MG1 functioning as the generator as the sum of abase torque Tgb and a PI controlled value Tgf through voltage feedbackof the driving circuits 191 and 192.

(3) Calculation of maximum amount of power consumption Pmmx: The processcalculates a maximum amount of power consumption Pmmx by the motor MG2.

(4) Calculation of target torque Tm: The process calculates a targettorque Tm of the motor MG2, so as to make the amount of power generationby the motor MG1 balance with the amount of power consumption by themotor MG2.

The battery-less drive in the normal state is described below withreferring to the flowchart of FIG. 15. When the program enters thecontrol routine of FIG. 15, the procedure first reads the currentvehicle speed SPD, the amount of depression AP of the accelerator pedal,and the revolving speed Nd of the drive shaft (that is, the axle) atstep S400, and determines the target revolving speed NE* of the engine150 based on these inputs at step S410. The concrete process of stepS410 reads the target revolving speed NE* of the engine 150 from a mapprovided in advance. Here the map is different from the map for controlin the state of failure shown in FIG. 7 but is set according to thedriving efficiency of the engine 150.

The procedure then reads the values of the respective sensors to obtainthe revolving speeds Ng and Nm of the motors MG1 and MG2 and the currenttorque Tmi−1 of the motor MG2 at step S420. Here the subscript ‘i−1’represents the current observed value, and the subscript ‘i’ representsthe controlled value to be output.

The procedure then successively calculates the required output of powergeneration Pgr at step S430, the target torque Tgi of the motor MG1 fromthe base torque Tgb and the voltage feedback controlled torque Tgf atsteps S440 and S450, the maximum amount of power consumption Pmmx atstep S460, and the target torque Tm of the motor MG2 at step S470. Thedetails of these processes are discussed below.

(1) Process of Calculating Required Output of Power Generation Pgr (StepS430)

The process first calculates energy Pm currently consumed by the motorMG2 from the revolving speed and the torque obtained at step S420according to Equation (11) given below:

Pm=(2π/60)×Nm×Tmi−1  (11)

The process then reads a current loss Pml of the motor system MG2corresponding to the revolving speed Nm and the current torque Tmi−1 ofthe motor MG2 from a loss map. The loss of the motor system increaseswith an increase in torque and with an increase in revolving speed. Oneexample of the loss map is shown in FIG. 16.

The process subsequently reads a current loss Pgl of the generatorsystem corresponding to the revolving speed Ng and the current torqueTgi−1 of the motor MG1 functioning as the generator from a similar lossmap. The process then calculates the required output of power generationPgr according to Equation (12) given below:

Pgr=−Pm−Pml−Pgl−Pdc  (12)

In Equation (12), Pdc denotes a loss of the converter 252. Although theloss Pdc can be regarded as a fixed value, for the enhanced accuracy,the loss Pdc may be read corresponding to the voltages on the higherside and the lower side and the consumed electric current on the lowerside from a map. The above series of processing gives the requiredoutput of power generation Pgr according to Equation (12).

(2) Process of Calculating Target Torque Tgi of Generator (Steps S440and S450)

The target torque Tgi of the motor MG1 functioning as the generator isobtained as the sum of the base torque Tgb and the voltage feedbackcontrolled torque Tgf as expressed:

Tgi←Tgb+Tgf  (13)

The base torque Tgb is obtained by simplified calculation of Equation(14) given below, based on the fundamental relation of energy=revolvingspeed×torque:

Tgb=(60/2π)×Pgr/Ng  (14)

The base torque Tgb of the motor MG1 functioning as the generator isnamely obtained by dividing the required output of power generation Pgr,which represents the amount of electric power to be generated by themotor MG1, by the revolving speed Ng of the motor MG1. The processing ofstep S440 calculates the base torque Tgb according to Equation (14).

The process subsequently calculates the voltage feedback controlledtorque Tgf. The calculation specifies the PI controlled value Tgfaccording to a difference ΔV between the observed voltage of powergeneration of the motor MG1 and a target voltage level. The motor MG1 issupposed to generate the required output of power generation Pgr, whichis calculated at step S430 and expected to be consumed by the motor MG2.The amount of power generation is thus supposed to balance the amount ofpower consumption. The loading of the motor MG2, however, abruptlychanges due to the varying road surface and other factors. Powergeneration of only the required output accordingly causes an excess oran insufficiency in generated output with a variation in loading. Thisleads to an abrupt change of the voltage between the power lines L1 andL2. The procedure accordingly measures the d.c. voltage of the powerlines and carries out feedback control to quickly compensate for thevoltage variation. The processing of step S450 adds the PI controlledvalue Tgf through the feedback of the d.c. voltage to the base torqueTgb, so as to specify the target torque Tgi of the motor MG1.

(3) Process of Calculating Maximum Amount of Power Consumption Pmmx(Step S460)

The process first obtains a limit torque or maximum torque Tgmx of themotor MG1 functioning as the generator. The maximum torque is read froma torque map shown in FIG. 17. The torque Tg of the motor MG1 isspecified by the revolving speed Ng and the voltage Vm. In the case ofpower generation via the driving circuit 191 functioning as theinverter, the torque Tg at a predetermined revolving speed Ng is reducedwith a decrease in voltage Vm. The maximum torque thus obtained may,however, not be fully taken out of the motor MG1. The torque of themotor MG1 functioning as the generator is the reactive torque againstthe torque of the engine 150 and can thus not exceed the output torqueof the engine 150. The maximum torque Tgmx read from the torque map ofFIG. 17 is accordingly restricted to a maximum torque Temx of the engine150. In the case where the maximum torque Temx of the engine 150 is lessthan the maximum torque Tgmx read from the torque map of FIG. 17, themaximum torque Temx of the engine 150 is set to the maximum torque Tgmxof the motor MG1. In the mechanical distribution type hybrid vehicle ofthe embodiment, the torque Tg of the motor MG1 and the torque Te of theengine 150 hold the following relation:

Tg=(1+ρ)×Te/ρ  (3a)

This corresponds to the case where Ts=Tg and Tc=Te in Equation (3). Inthis embodiment, Tg=Te/3.6.

Here the maximum torque Temx of the engine 150 is read from a torque mapprovided in advance. One example of the torque map is shown in FIG. 18.The maximum torque Temx of the engine 150 is set with regard to therevolving speed Ne and the cooling water temperature THW of the engine150 as parameters. In the graph of FIG. 18, a solid curve WU representsthe revolving speed-torque characteristic at the warm-up time and abroken curve CS represents the revolving speed-torque characteristic atthe cold time. Strictly speaking, the maximum torque Temx of the engine150 is affected by the altitude (that is, the difference in air density)and the temperature of intake air. These parameters may be reflected onthe maximum torque Temx in a multi-dimensional version of the torque mapshown in FIG. 18. The maximum torque Temx read from the torque map ofFIG. 18 may alternatively be corrected with the altitude and thetemperature of intake air.

After determining the maximum torque Tgmx of the motor MG1 restricted tothe maximum torque Temx of the engine 150, the process obtains a lossPglmx under such output conditions (that is, the revolving speed Ng andthe torque Tgmx). The loss Pglmx of the motor MG1 is read correspondingto the revolving speed Ng and the maximum torque Tgmx from the loss mapof FIG. 16 as in the case of the loss of the motor MG2. The process thencalculates maximum generated energy Pgmx of the motor MG1 functioning asthe generator from the maximum torque Tgmx and the revolving speed Ngaccording to Equation (15) given below:

Pgmx=(2π/60)×Ng×Tgmx  (15)

The current loss Pml of the motor system has already been read from theloss map of FIG. 16. The maximum energy Pmmx consumed by the motor MG2is calculated from the maximum generated energy Pgmx of the motor MG1functioning as the generator, the loss Pglmx of the motor MG1 and theloss Pml of the motor MG2. The maximum energy Pmmx consumed by the motorMG2 is accordingly equal to the remainder obtained by subtracting thelosses from the maximum generated output:

Pmmx=Maximum generated output−Losses

=−Pgmx−Pml−Pglmx−Pdc  (16)

Here the maximum generated output Pgmx of the motor MG1 has the minussign. This is because the consumed energy is expressed as the plus signand the generated energy is expressed as the minus sign in theequations.

The energy balance is expressed as:

I×V=(Pm+Pml)+(Pg+Pgl)+Pdc  (17)

The first term on the right side represents the sum of the consumedenergy and the loss in the motor MG2, the second term represents the sumof the generated energy and the loss in the motor MG1, and the thirdterm represents the loss of the converter 252. When it is assumed thatall the generated electric power is consumed by the motor, I×V=0 inEquation (17). Namely Equation (17) is rewritten as:

Pm=−Pg−Pml−Pgl−Pdc  (18)

Whereas Equation (16) gives the maximum consumed energy under theconditions of the maximum torque and the maximum loss, Equation (18)gives the consumed energy at the time of stationary drive and isessentially equivalent to Equation (12).

(4) Process of Calculating Target Torque Tm of Motor MG2 (Step S470)

At the final stage in the series of the processing, the processdetermines a required torque Tmr of the motor MG2. The required torqueTmr is calculated by subtracting a direct torque (Te/ρ) from a requiredtorque Td of the axle as expressed:

Tmr=Td−Te/ρ  (19)

The required torque Td of the axle is read from a vehicle requirementtorque map shown in FIG. 19. This map gives the required torque Td ofthe axle against the vehicle speed with regard to the depression amountAP of the accelerator pedal (or the throttle opening θ) as a parameter.The direct torque is a specific portion of the torque Te of the engine150 transmitted to the axle and is defined as Te/ρ according to Equation(5) given above.

The process then restricts the required torque Tmr of the motor MG2 thusobtained to an upper limit torque Tmmx. The upper limit torque Tmmx iscalculated from the maximum consumed energy Pmmx of the motor MG2specified by Equation (16) and the revolving speed Nm of the motor MG2according to Equation (20) given below:

Tmmx=(60/2π)×Pmmx/Nm  (20)

The required torque Tmr of the motor MG2 determined by Equation (19) iscompared with the upper limit torque Tmmx specified by Equation (20).The process restricts the required torque Tmr to the upper limit torqueTmmx and specifies the target torque Tm of the motor MG2 as:

Tm←Tmr(Tmr≦Tmmx)

Tm←Tmmx(Tmr>Tmmx)  (21)

Referring back to the flowchart of FIG. 15, the procedure outputs thetarget torque Tm of the motor MG2 thus obtained at step S480. Thecontrol routine of FIG. 15 regulates the target torque Tgi of the motorMG1, which functions as the generator, based on the basic torque Tgb andthe voltage feedback controlled torque Tgf (step S450), and regulatesthe target torque Tm of the motor MG2 based on the maximum consumedenergy Pmmx of the motor MG2, which is obtained by subtracting thelosses from the maximum generated output according to Equation (16)(step S480). The revolving speed Ne of the engine 150 is under thefeedback control by the engine ECU 240. This arrangement makes theamount of power generation by the motor MG1 balance with the amount ofpower consumption by the motor MG2 and thus enables the vehicle to bedriven without charging or discharging the HV battery 194. The motor MG1functioning as the generator is subject to the feedback control with thecontrolled value Tgf based on the difference ΔV between the observedd.c. voltage of power generation and the target voltage. This feedbackcontrol ensures a quick response to the voltage variation andeffectively actualizes the battery-less drive, which has not beensufficiently attained by the simple balance of the power generation withthe power consumption.

H. Control Procedure in State of Weldinq Failure of System Main

Relay

The following describes the control procedure in the state of weldingfailure of the system main relay SMR as an application of theembodiment. The cause of the welding failure of the system main relaysSMR1, SMR2, and SMR3 and the method of detecting the welding failurehave been discussed already. FIG. 20 is a flowchart showing a drivecontrol routine executed in the state of welding failure of the systemmain relay SMR. In the end of this drive control routine, the proceduredetects a welding failure of the system main relay SMR3 at the timingspecified in FIG. 4B at step S500 and registers the welding failure inthe abnormality record registration circuit 280 at step S510. When anext drive of the vehicle starts, the program enters this drive controlroutine of FIG. 20. The procedure first reads the contents of theabnormality record registration circuit 280 and determines whether ornot the system main relay SMR3 has a welding failure at step S600. Whenthere is a welding failure in the system main relay SMR3, the procedurelights the diagnosis lamp 291 on and successively closes the system mainrelays SMR1 and SMR2 to connect the HV battery 194 with the power linesL1 and L2 at step S610 as in the case of the control procedure in thenormal state. When there is no welding failure in the system main relaySMR3, on the other hand, the procedure carries out the drive control inthe normal state at step S680.

In the state of the welding failure, after closing the system mainrelays SMR1 and SMR2, the procedure activates the engine 150 at stepS620 as in the case of the control procedure in the normal state. Oncethe engine 150 is activated, the vehicle can be driven in thebattery-less drive mode as discussed in the above embodiment. Theprocedure accordingly waits until the driving state of the engine 150satisfies desired conditions at step S630. When the driving state of theengine 150 meets the desired conditions, the procedure opens the systemmain relays SMR1 and SMR2 to allow a shift to the battery-less drivemode at step S640. In either case, when the drive of the vehicle isterminated (steps S650 and S690), the procedure again detects thewelding failure of the system main relays SMR3 and registers the weldingfailure if detected (steps S500 and S510).

In the application of the embodiment described above, when a weldingfailure arises in the system main relay SMR3, the control procedureconnects the HV battery 194 with the power lines L1 and L2 for a shorttime period until the engine 150 is activated. Once the engine 150 isactivated, the HV battery 194 is disconnected from the power lines L1and L2, and the vehicle is driven in the battery-less drive mode. In thecase where the vehicle is involved in some traffic accident, the vehiclestops to terminate the power generation and lose the voltage on thepower lines L1 and L2. This protects the driver, mechanic, or anyrelated people from electric shocks. In the battery-less drive mode, theHV battery 194 is separated from the power lines L1 and L2, so that thehigh voltage of the HV battery 194 is not applied to the power lines L1and L2.

I. Structure of Electrical Distribution Type

The above description regards the mechanical distribution-type parallelhybrid vehicle that distributes the power of the engine 150 by means ofthe planetary gear 120. The technique of the present invention is alsoapplicable to the electrical distribution type hybrid vehicle that usesa pair-rotor motor including a pair of rotors rotatable relative to eachother, in order to actualize a similar battery-less drive. FIG. 21schematically illustrates the structure of a power output system in theelectrical distribution type hybrid vehicle. In this power outputsystem, one rotor of a clutch motor 330, which attains a variablesliding speed between two rotors, is connected to the crankshaft 156 ofthe engine 150. The other rotor of the clutch motor 330 is connected tothe drive shaft. An assist motor 340 is also linked with the driveshaft. In the electrical distribution type power output system, theclutch motor 330 and the assist motor 340 are driven via the invertercircuits as in the structure of the embodiment. The vehicle is driven inthe battery-less drive mode as in the case of the above embodiment, inwhich the on-off control of the inverter circuit connected to the clutchmotor 330 is terminated and the power generation utilizing the counterelectromotive force is carried out with electric current via theprotection diodes disposed in the inverter circuit.

J. Change of Drive Mode

The hybrid vehicle may be driven while changing the drive mode. FIG. 22shows a change of the drive mode. The hybrid vehicle changes the drivemode from a normal drive mode NDM without any failure or abnormality toa battery-less drive mode IBL using the first and the second drivingcircuits 191 and 192 constructed as the inverters, in response todetection of a failure in the HV battery 194 (on the assumption that theuse of the first driving circuit 191 is allowed) or in response todetection of a welding failure in the system main relay SMR3. Thebattery-less drive mode IBL opens the system main relays SMR1 and SMR2to disconnect the HV battery 194 from the power line L1. In the case ofthe welding failure in the system main relay SMR3, the procedure closesthe system main relays SMR1 and SMR2 and activates the engine 150, priorto the shift to the battery-less drive mode IBL as described in detailin ‘H. Control Procedure in State of Welding Failure of System MainRelay’. The details of the battery-less drive mode IBL using the firstand the second driving circuits 191 and 192 functioning as the invertersare described in ‘G. Battery-less Drive in Normal State of Inverters’and are thus not specifically described here.

The hybrid vehicle changes the drive mode from the battery-less drivemode IBL to a counter electromotive force power generation drive modeRVL when the first driving circuit 191 fails to prohibit furtherswitching operations, when the vehicle goes back in a range R in thestructure of the mechanical distribution type, or when some disturbancelowers the voltage under the control in the battery-less drive mode IBL.The details of the counter electromotive force power generation drivemode RVL are described in ‘F. Control Procedure in Response to Detectionof Failure’. This drive mode RVL sets the target revolving speed NE* ofthe engine 150 according to the loading and causes the motor MG1 tocarry out power generation utilizing the counter electromotive force. Inthe case of the reverse drive in the range R in the structure of themechanical distribution type, the drive mode is shifted to the counterelectromotive force power generation drive mode RVL, in order to preventthe direct torque of the engine 150 from being inverse to and therebycanceling the driving torque of the drive shaft. The drop in voltage ofpower generation occurs in the case where the voltage feedback controlfails to recover the voltage level when a delay of the power generationcontrol against a disturbance or another factor abruptly lowers the d.c.voltage or when the significantly low temperature of the engine 150abruptly lowers its revolving speed. The voltage drop decreases theoutput torque (see FIG. 17), and the insufficient output torque does notallow recovery of the voltage level. In such cases, the drive mode isshifted to the counter electromotive force power generation drive modeRVL to stop the switching operations of the first driving circuit 191.This raises the inter-terminal voltage of the motor MG1 and causes powergeneration utilizing the counter electromotive force. When the voltageis recovered to a sufficient level for power generation via theswitching operations of the inverters, the drive mode is returned to thebattery-less drive mode IBL using the inverters. When there is a failurein the first driving circuit 191, the vehicle directly changes the drivemode from the normal drive mode NDM to the counter electromotive forcepower generation drive mode RVL.

The hybrid vehicle changes the drive mode from the counter electromotiveforce power generation drive mode RVL to a battery drive mode BDM whenthe HV battery 194 has a sufficient high voltage as its state of chargeSOC. In the battery drive mode BDM, the first driving circuit 191 is notusable while the use of the second driving circuit 192 is allowed, sothat the vehicle is driven as the electric vehicle. At the time ofstopping the vehicle driven in this battery drive mode BDM, the motorMG2 carries out the regenerative operation to regenerate the electriccurrent and charges the HV battery 194 via the second driving circuit192. This recovers the state of charge SOC of the HV battery 194. Whenthe voltage of the HV battery 194 gradually decreases to or below aspecific level, at which the HV battery 194 can not actuate theconverter 252 (approximately 140 volts in the embodiment), the drivemode is returned to the counter electromotive force power generationdrive mode RVL. In the battery drive mode BDM, a braking operationensures a braking force corresponding to engine brake and besidesenables the braking energy to be regenerated as electric power.

When engine brake is required in the course of deceleration or when thevehicle fails to climb a steep ascent and goes back, the vehicle changesthe drive mode from the battery-less drive mode IBL using the invertersto a motoring drive mode EBM. In the course of deceleration, themotoring drive mode EBM cuts off the supply of fuel to stop combustionof the fuel in the engine 150 and uses the motor MG2 as the generator toregenerate the braking energy in the form of electric power. Theregenerated energy is consumed by the power operation of the motor MG1to motor the engine 150. When the vehicle goes back unintentionally on asteep ascent, the axle rotates reversely and the motor MG2 functions asthe generator. It is thus required to cancel the restriction of thetorque, which is calculated from the power of the motor MG1 supposed tofunction as the generator, to the upper limit torque Tmmx. In suchcases, the electric power generated by the motor MG2 is also consumed bythe power operation of the motor MG1 to motor the engine 150.

When the vehicle speed is reduced to decrease the consumable energy formotoring and the regenerative electric power becomes greater than theconsumed electric power for motoring, the vehicle changes the drive modefrom the motoring drive mode EBM to a zero torque drive mode TZM wherethe target torque Tm of the motor MG2 is set equal to zero. In the zerotorque drive mode TZM, the vehicle is subject to no regeneration ofelectric power nor motoring.

The hybrid vehicle is driven while changing the drive mode in the abovemanner. Among the various drive modes, the normal drive mode NDM has thegreatest output. The battery-less drive mode IBL using the inverters hasthe greater output than the counter electromotive force power generationdrive mode RVL. It is not necessary to adopt all the drive modes shownin FIG. 22. Any combination of required drive modes may be appliedaccording to the design and other requirements of the vehicle. Anotherpossible modification provides a greater number of drive modes andchanges the drive mode at a greater number of stages according to therequirements.

The above description regards the application of the present invention,some embodiments according to the present invention, and controlprocedure of changing the drive mode. The above description is, however,to be considered in all aspects as illustrative and not restrictive.There may be many modifications, changes, and alterations withoutdeparting from the scope or spirit of the main characteristics of thepresent invention. All changes within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

The scope and spirit of the present invention are indicated by theappended claims, rather than by the foregoing description.

What is claimed is:
 1. A hybrid vehicle with an engine, a generator, anda motor mounted thereon, said engine outputting power through combustionof a fuel, said generator provided with permanent magnets generatingelectric power with at least part of the power output from said engine,said motor outputting power to a drive shaft of said hybrid vehicle,said hybrid vehicle comprising: an engine control unit that feedbackcontrols a quantity of the fuel injected to said engine to attain aspecified target if revolving speed of said engine; a power generationcontrol unit that causes said generator to carry out power generationutilizing a counter electromotive force; a loading detection unit thatspecifies a loading applied to said hybrid vehicle; a generatorrotational speed variation unit that varies a rotational speed of saidgenerator, based on the specified loading; and a motor driving unit thatdrives said motor with the electric power generated by said generator atthe varying rotational speed.
 2. A hybrid vehicle in accordance withclaim 1, said hybrid vehicle comprising: an inverter that switcheselectric current running through a multiphase coil of said generator; asecondary battery that is charged with the direct current converted bythe switching operation of said inverter: an abnormal state detectionunit that detects an abnormal state, which does not allow said secondarybattery to be charged via said inverter; and an abnormal-state controlunit that carries out a specific control, which causes said powergeneration control unit, said generator rotational speed variation unit,and said motor driving unit to implement their functions, in response todetection of the abnormal state by said abnormal state detection unit.3. A hybrid vehicle in accordance with claim 2, said hybrid vehiclefurther comprising: an operation unit that prohibits the powergeneration utilizing the counter electromotive force via said powergeneration control unit but drives said motor with electric poweraccumulated in said secondary battery, when an observed voltage level ofsaid secondary battery is higher than the counter electromotive forceutilized for the power generation via said power generation controlunit.
 4. A hybrid vehicle in accordance with claim 1, said hybridvehicle further comprising: a target revolving speed setting unit thatspecifies the target revolving speed of said engine transmitted to saidengine control unit, based on behavior of an accelerator pedal.
 5. Ahybrid vehicle in accordance with claim 1, wherein said generatorrotational speed variation unit increases the rotational speed of saidgenerator with an increase in amount of depression of an acceleratorpedal.
 6. A hybrid vehicle in accordance with claim 1, wherein saidgenerator rotational speed variation unit lowers or raises the targetrevolving speed of said engine in response to detection of an increasingtendency or a decreasing tendency of an actual revolving speed of saidengine relative to the target revolving speed of said engine transmittedto said engine control unit.
 7. A hybrid vehicle in accordance withclaim 2, wherein said abnormal state detection unit detects the abnormalstate and activates said abnormal-state control unit to carry out thespecific control, when an external force makes the drive shaft inverselyrotated and said motor fall into a state of power generation.
 8. Ahybrid vehicle in accordance with claim 1, wherein said motor drivingunit comprises: a maximum electric power setting unit that sets amaximum electric power generated by said generator with the power ofsaid engine; a driving electric power computation unit that specifiesdriving electric power consumed for driving said motor within the presetmaximum electric power, based on the specified loading; a powergeneration unit that causes said generator to generate electric powerthat is equivalent to the driving electric power consumed by said motor;and a current regulation unit that regulates electric current runningthrough a multiphase coil of said motor with the generated electricpower.
 9. A method of controlling a hybrid vehicle, wherein an engineoutputs power through combustion of a fuel, a generator provided withpermanent magnets generate electric power with at least part of thepower output from said engine, and a motor is driven with at least partof the electric power generated by said generator, so as to output powerto a drive shaft of said vehicle, said method comprising the steps of:feedback controlling a quantity of the fuel injected to said engine toattain a specified target revolving speed of said engine; causing saidgenerator to carry out power generation utilizing a counterelectromotive force; specifying a loading applied to said hybridvehicle; varying a rotational speed of said generator, based on thespecified loading; and driving said motor with the electric powergenerated by said generator at the varying rotational speed.